1. Technical Field
This invention generally relates to trailers. More particularly the invention relates to cross-members of semi-trailers. Specifically, the invention relates to a cross-member for a trailer that comprises an elongate tube with a planar member extending through the bore thereof and being connected to an interior surface thereof, and where the cross-member is relatively inflexible in bending and tension, while remaining relatively flexible overall in torsion.
2. Background Information
Trailer frames usually consist of two longitudinal frame rails that are joined together by cross-members at intervals along their length. The cross-members are essential not only to hold the longitudinal rails together, but are also used at points where concentrated loads are put into the longitudinal rails, such as the regions on the frame where the kingpin, suspension and body are mounted. Trailers, particularly trailers designed to carry construction materials such as gravel, asphalt, boulders, debris, etc., may be taken over terrain that is not very smooth. When the tires on one side of the trailer are raised or lowered with respect to the other side of the trailer and to the kingpin, such as during diagonal axle-walk, a relative twist is put into the longitudinal rails. This twisting motion, or torsion, can lead to failure of the rails and/or members of the frame.
Generally, there are two approaches to handling twisting between the longitudinal rails. The first approach is that the frame cross-members can be made torsionally strong and rigid in order to resist sizeable twisting loads. Torsionally rigid cross-members will tend to have a solid or tubular cross-sectional shape that is generally of a circular or square configuration. One problem experienced with torsionally rigid cross-members is that the torque, carried from one side of the trailer to the other by the cross-members, also induces a stress into the rails. This stress is frequently at the same position as the maximum, or nearly maximum, bending stress. Making trailer frame cross-members strong enough and rigid enough to resist these substantial twisting loads usually requires that additional material or a different material be used to construct the cross-members. These cross-members are often manufactured to be heavier and/or stronger. Using additional or costlier materials tends to raise the overall price of the trailer, thus reducing the profit margin for the manufacturer. Also, using additional materials has the side-effect of reducing the possible legal payload that the trailer can ultimately carry because of weight restrictions. This tends to cut into the operator profits.
The second approach taken to handling twisting is to make the frame cross-members torsionally flexible so that they tend to flex and bend under sizeable twisting loads. Flexible cross-members typically have an open-type of cross-sectional shape, such as that of an I-beam or a member with a channel along its length. However, utilizing flexible cross-members to resist the twisting loads also has shortcomings. This is particularly true when the cross-members are used for supporting primarily vertical loads such as attaching the body to the frame. If the vertical load is supported at a lateral position, i.e., at a position other than directly over the longitudinal frame rails, then a bending moment and its consequent bending stress are induced in the cross-member at its connection zone with the longitudinal frame. In these instances, the maximum torsional stress induced by the twist between the two longitudinal frame rails will also tend to coincide with the maximum bending stress as is the case with torsionally rigid cross-members. This combination of stresses can lead to failure of the rails and cross-members of the trailer.
There is therefore a need in the art for an improved cross-member for use in the manufacture of trailer frames.